The company said for the quarter ending Nov. 3 it expects "slightly negative" same-store sales, from previous guidance of a 1 percent to 3 percent rise.

Same-store sales, or sales at stores open at least a year, is a key indicator of retailer performance since it measures growth at existing stores rather than newly opened ones.

Despite the warning, Big Lots said due to operating profit improvement and inventory and expense management, it expects third-quarter earnings to be at the high end of its guidance between 9 cents and 13 cents per share.

Analysts polled by Thomson Financial expect a profit of 12 cents per share.

Sales of toys, home and fall seasonal merchandise have been below expectations, while furniture, consumables and hardlines have done better, Big Lots said. Hardline, or non-textile merchandise, includes electronics, furniture, sporting goods and other products.

Western and Southeastern regions have shown weakness while Central region sales have been better, Big Lots said.

JPMorgan analyst Charles Grom said in a note to investors Thursday he was "a bit concerned" that the third-quarter softness could become a trend as same-store sales slow and the company faces more difficult comparisons.

The types of items that are selling well are a red flag, the analyst said.

"The best performing categories in the third quarter included lower margin consumables and hardlines with higher margin home and seasonal products trending negative," Grom wrote. "(This is) reminiscent of low-end peer Dollar General -- this rising mix of lower margin items will likely pressure the company's gross profit margin line."

Shares fell $4.50, or 16.4 percent, to close at $23.02 Thursday. The stock has traded between $19.81 and $36.15 during the past 52 weeks.